It  returns arc tangent of two variables

<?php
echo atan2(17,17);
?>

Output

0.78539816339745

It returns  Inverse hyperbolic sine

Example

<?php
echo asinh(.90);
?>

Output

0.80886693565278

It returns  arc sine

Example

<?php
echo asin(.90);
?>

Output

1.1197695149986

It returns  Inverse hyperbolic cosine

Example

<?php
echo acosh(90);
?>

Output

5.1929259852637

It returns arccosine value

Example

<?php
echo acos(.90);
?>

Output

0.45102681179626

It returns absolute value

Example

<?php
echo $abs = abs(-1.7);
?>

Output

1.7